The rainforests of Borneo, which are some of the world’s tallest, most carbon-dense and diverse forests, have been accruing carbon over the past 50 years, according to a new study published in the journal Nature Communications. The study, led by the University of Leeds, quantifies for the first time the role of South East Asian tropical rainforests in the fight against climate change.

An international team of more than 50 scientists monitored tens of thousands of trees across Borneo for up to half a century, revealing the rainforest’s steady increase in forest biomass — 430kg per hectare per year — as well as its vulnerability to climate and land-use changes.

Lead author Dr Lan Qie said, “Borneo’s remaining rainforests are increasing in size, adding to their already high carbon stocks. The average increase we saw in Borneo is equivalent to adding 700 household Christmas trees to each 100m square area of forest, each year.”

Trees in Lambir Hills National Park on Borneo

The new results are consistent with increases shown across tropical Africa and Amazonian forests. Co-author Professor Simon Lewis said, “After conducting dozens of field campaigns across the tropics over the past two decades, we can now finally say that the world’s remaining intact tropical forests, across the Amazon, Africa and Asia, are all acting as carbon sinks – absorbing more carbon than they are releasing. It is now clear that undisturbed tropical rainforests across the world are all providing an important service to humanity in removing carbon from the atmosphere, adding a further reason to protect these vulnerable forests.”

Yet, the study highlights two threats to continued carbon uptake by rainforests: droughts and forest fragmentation. The research monitored the 1997-1998 El Niño drought which killed many trees in Borneo, returning carbon to the atmosphere, and halting its ability to act as a carbon sink. This illustrates the risk posed by future droughts, which climate models suggest will become more severe and frequent, causing a temporary pause in the rainforest carbon sink.

Forested areas of Borneo differ from the large tracts of forest found in the Amazon and Congo basins; in South East Asia these forests are highly fragmented - patches of forests are often isolated from the larger forest tracts by burnt land, oil palm plantations or farmers’ fields. This study highlights that monitored forest areas close to edges tended to lose carbon to the atmosphere.

CEH-based co-author of the study, Dr Lindsay Banin, explained that “the remaining tropical forests of Southeast Asia are clearly critical to climate change mitigation, but the nature of their distribution in space and the impact of big disturbances such as drought are also important in determining key ecosystem processes such as carbon capture – these findings can help direct strategies for ensuring forest resilience into the future”.

The remaining tropical forests of Southeast Asia are clearly critical to climate change mitigation, but the nature of their distribution in space and the impact of big disturbances such as drought are also important in determining key ecosystem processes such as carbon capture..." Dr Lindsay Banin, Centre for Ecology & Hydrology

Near forest edges the stands tended to lose carbon to the atmosphere. Trees were more likely to die if they were closer to the edge, and the tree species that replace them tended to be those that store less carbon. CEH PhD students Emily Waddell (University of York) and Robin Hayward (University of Stirling) are currently investigating further the processes of plant community change in disturbed forests of northern Borneo.

Dr Lan Qie added: “Our calculations indicate a minimum size that a patch of forest must be in order for it to be a carbon sink - where its interior is absorbing enough carbon to outweigh its edges, which may be losing carbon. A forest reserve of 300 hectares, or one square mile, is just about big enough.” As such, preserving and enhancing tracts of continuous forest is really important. Buffer zones may also be employed to reduce the carbon loss at forest edges, allowing forest fragments of any size to contribute to the protection of carbon stocks and biodiversity.

Additional information

The research paper 'Long-term carbon sink in Borneo’s forests halted by drought and vulnerable to edge effects' is published on 19 December 2017 in the journal Nature Communications. DOI: 10.1038/s41467-017-01997-0

The research was conducted by a global team of more than 50 scientists, drawing on work dating back to the 1960s. The work was supported by a European Research Council grant awarded to Professor Oliver Phillips and Professor Simon Lewis, both at the University of Leeds.

CEH scientist Lindsay F Banin is a plant and ecosystem ecologist at CEH's Edinburgh site with a particular interest in forest systems and the impact of environmental changes on their function.

See also

A blog post by Lindsay Banin about a special issue of Plant Ecology & Diversity journal looking at the ecology of the Asian Dipterocarps.